The present invention relates generally to emulsion coating compositions and specifically to a solvent resin enamel having water dispersed therein.
It has been a desideratum in the art to provide water-in-oil emulsion solvent resin enamel compositions which are capable of producing coatings having good hiding power or high gloss, and which are possessed with an adequate shelf life for commercial use. These enamels include water as part of the evaporative vehicle and comprise a dispersion, through the use of suitable emulsifying agents, of up to 80% by weight of water in a solution of organic solvents and a solvent soluble film-forming resin. The compositions further contain organic and inorganic polar pigments to impart color to the resultant film or coating. The dispersion of water in such compositions is not without problems where a polar pigmented enamel coating is desired.
While water-in-oil emulsion coating compositions have produced high gloss clear films and non-polar pigmented enamel coatings having a gloss of seventy units or above on a 60.degree. gloss meter, when polar pigments are dispersed in the water-in-oil solution resin compositions the resultant gloss was found to be lower. In addition, it was found that after the initial mixing and testing of the polar pigmented enamels, the gloss of the coating produced by the enamel deteriorated with age. For example, after the enamel became a few days old, the composition deteriorated to the extent that it produced a gloss of only twenty to thirty units as compared to nearly eighty when the cans were one day old. Examination of the drying film of these enamels established that the loss of gloss was caused by pigment flocculation due to the adsorption of water on the surface of each pigment particle. During storage, the emulsified water is able to penetrate the organic surfactant which became attached to each pigment particle during the dispersion process, and disrupt the balance of the electrical charges within the paint system. This results in large pigment flocs being formed during the time that the enamel is passing through the drying stage i.e. from a wet condition to a tacky condition. Aside from the above-described problems with gloss enamels, such polar pigment flocculation has caused pigment dispersion problems in both semi-gloss and flat water-in-oil emulsion enamel paints.